Probe-tube microphone measurements with very young infants.

The practicalities of performing probe-tube microphone measurements in a clinical environment with unsedated infants were examined. External ear resonance curves (unaided response) were obtained for both ears of a group of infants aged 0-6 months and an adult comparison group. A repeat measure (with probe-tube repositioning) was made to estimate the test-retest reliability of these measures. Results showed that the mean infant resonance frequency (4200 Hz) occurred at a significantly (P less than 0.005) higher frequency than the mean adult resonance frequency (2950 Hz). Infants test-retest differences for resonance frequency (mean = 286 Hz, s.d. = 404 Hz) and size of peak (mean = 2.2 dB, s.d. = 2.6 dB) showed acceptable stability for the measurements. Size of resonance peak was found to vary positively with ear canal volume; however, estimation of ear canal volume from tympanometry did not provide a useful indicator of the size of the peak. The probe-microphone measurements were found to be feasible, repeatable and practical with these infants.